[RFC/PATCHv0 2/4] fast-import.c:do_change_note_fanout(): Also apply load_tree() to initial root

TODO: tests!

do_change_note_fanout() recursively traverses a "struct tree_entry" data structure. Before recursively traversing into a subtree, we make sure to call load_tree() on that subtree. However, for the initial/root struct tree_entry object, we assumed that load_tree() had already been invoked by our caller. This is true, except in the following case:

If we load a previously written notes tree using 'filemodify' instead of 'from' [1], then we do not pass the notes ref to load_branch() (which takes care of calling load_tree() on the root tree_entry).

When load_tree(root) has not been called before the first 'notemodify' command is parsed, the for loop in do_change_note_fanout() does nothing, and we end up not counting the existing notes, which ends up producing a notes tree with mixed/insufficient fanout.

Fix this by always making sure to call load_tree() at the start of do_change_note_fanout(). Since load_tree() is now called before the for loop, we no longer need to call load_tree() on a subtree before recursing into it, the recursive call will take care of its own load_tree().

[1]: Usually, when adding notes to an existing notes tree, one would use a
     'from' command like this:

         from refs/notes/foo^0

     However, if one does not want to retain notes history (i.e. one wants
     the current refs/notes/foo commit to be build without any parents),
     then one can replace the 'from' command with the following 'filemodify'
     "hack" to pre-load the existing notes tree without using it as a parent:

         M 040000 refs/notes/foo^{tree} \n

Discovered-by: Mike Hommey <mh@glandium.org>
Signed-off-by: Johan Herland <johan@herland.net>
---
 fast-import.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)